This invention relates to GaAs devices and more particularly to a means and method for providing a simple, reliable n.sup.+ contact for such devices.
Heretofore various methods have been used to form contacts on GaAs devices. These include an epitaxy n.sup.+ layer deposited on a n.sup.+ GaAs substrate. The n.sup.+ layer is etched in areas other than in the contact regions to get down to the n layer. This process involves complicated chemical deposition equipment which has inherent limitations for large surface devices. Another method involves implanting ions directly into the n GaAs to form an n.sup.+ layer in a planar format. High-temperature annealing is required to activate the implanted n.sup.+ species and an adequte encapsultant has not been developed to provide contacts of about 10.sup.18 ions/cc doping in reproducible format. N.sup.+ dopants may be diffused directly into the GaAs surface. This technique has not been applied successfully due to the high-temperature drive required and to the associated deleterious loss of As. Another method is to make use of an alloy system such as AuGeNi to form the n.sup.+ contact. AuGe is evaporated in an 88/12 composition ratio followed by a thin Ni overcoat to prevent "balling up" during sintering with the substrate. This process is not reliable and has reproducibility problems.